Controlled atmosphere storage of fresh produce utilizes high levels of CO2 and reduced oxygen to increase the shelf life of the product. Modified atmosphere packaging is used to enhance the lifetime and/or the quality of food by reducing the amount of oxygen (towards zero) in the atmosphere compared to air. Fresh produce tends to be packed under an equilibrium modified atmosphere which uses high levels of CO2 and reduced levels of oxygen and which allows a reduced respiration rate.
VOCs include a range of compounds that are derived from organic matter. One example of a VOC derived from organic matter is ethylene, a plant hormone that causes ripening, whilst another example is trimethylamine, a gas commonly given off by fish as it decomposes.
The removal of VOCs derived from organic matter is of interest for a variety of applications. The adsorption of ethylene can prevent undesired ripening and softening, loss of colour, loss of leaves and sprouting to occur in fruit and vegetables, it is also known to prevent other food and horticultural products from perishing prematurely, and can help eliminate unpleasant smells. Various methods have been used to oxidise or combust VOCs using Pt on Al2O3 or KMnO4. However, although these systems are efficient for the removal of VOCs, they have disadvantages associated with their use. Pt on Al2O3 works by catalytically combusting the ethylene at elevated temperatures, therefore Pt on Al2O3 needs to be used in a heated unit separate from the source of the VOCs (see for example GB 2 163 637 A and U.S. Pat. No. 4,331,693). KMnO4 does not appear to remove VOCs efficiently from humid environments. Since organic matter, such as food, cannot be heated without being altered and inherently exudes moisture such systems are unsuitable for use in removing VOCs derived from organic matter.
Other methods used to remove VOCs are suited for use at lower temperatures; these include the use of high surface area supports, usually in conjunction with a promoter, for the adsorption of VOCs. For example, JP 2-261341 relates to the adsorption of ethylene from refrigerated storage compartments, JP 2-233381 relates to an ethylene adsorption film and JP 2000-004783 relates to a combined ethylene adsorber, deodoriser and anti-bacterial product for use in a refrigerator. Specific support materials are not disclosed in any of these publications, instead activated carbon and metal oxides are stated as being generally suitable for use as supports. GB 2 252 968 A relates to an adsorber comprising a sepiolite in combination with a zeolite, and optionally a metal selected from the platinum group metals, the iron group metals, group I metals, group VII metals and the rare earth metals. The most preferred zeolites for use in the invention described in GB '968, are silicalites because their alumina content is almost zero.
WO2007/052074 relates to the use of palladium doped ZSM-5 to adsorb VOCs derived from organic matter. WO2007/052074, however, does not describe the use of the palladium doped ZSM-5 in an environment comprising low or no gaseous oxygen.